Cholera afflicts both children and adults and cholera exists as an endemic disease in over 100 countries of the world. The death rate is highly dependent on the treatment facilities; the highest mortality rates are in Africa where case fatality rates have approximated 10%, especially during epidemic attacks. It is likely that cholera as an endemic infection causes 100,000 to 150,000 deaths annually. An ideal vaccine would provide a high level of long-term protection to even those at high risk for severe illness, e.g., people with blood group type "O". This protection would commence shortly following administration of a single oral dose. New oral vaccines have been developed for cholera, including both killed vaccines and live attenuated strains. An important step in the evaluation of these vaccines is the volunteer study in which non-immune healthy adult volunteers are immunized with the candidate vaccine and are then challenged with a typical cholera strain. This challenge has always been performed in a hospital study ward to insure accurate data collection and safety. Critical factors in the challenge model include the following: a) providing a known number of bacteria which have been prepared in a consistent and reproducible manner, b) giving these bacteria to the volunteers under controlled conditions, (e.g., fasting before and after challenge and providing a standard buffer solution at the time of the bacterial challenge), c) monitoring signs and symptoms objectively, especially fluid intake and output, d) providing appropriate medical treatment to the volunteers, especially rehydration fluids and antibiotics, and e) preventing spread of the challenge strain to others on the ward and outside the hospital with contact precautions and disinfection of stool and vomitus. A major constraint for multi-center studies has been the difficulty in preparing a consistent inoculum. Freshly prepared bacteria are difficult to standardize, and the results from different centers will be valid only if a method is developed which will guarantee that the inoculum is consistent from place-to-place and time-to-time. In the past it has been difficult to obtain reproducible results between different centers, and it is hoped that development of a standard inoculum and method for its administration will allow additional centers to carry out volunteer studies and for the results from different centers to be combined in multi-center studies. Based on the initial sample size estimates, the attack rate of 10/10 provides a 95% confidence interval that the true attack rate is between 69-100%. This is greater than the minimal efficacy (true attack rate > 50%) we accepted for our validation study. Based on these data, and the fact that our volunteers' geometric mean purge (3.3L) was similar to that seen in the prior studies performed in Baltimore, we believe that we have validated this challenge model. Furthermore, we have safely and successfully performed a cholera challenge study at Children's Hospital Medical Center and the University of CIncinnati. We have established the framework for subsequent studies at the Enteric Vaccine Program at Children's Hospital Medical Center. We plan to validate a similar model using an 0139 cholera challenge strain and to begin vaccine testing using this model during the next 1-2 years.